"Automakers don't necessarily need hybrids, [electric cars], or plug-ins," he said in an interview.

Several automakers are already using those technologies to boost the gas mileage of their vehicles, with manufacturers such as Ford introducing EcoBoost direct-injected, turbocharged engines in several models across its lineup.

Ford isn't the only one, either--virtually every car company currently has one or more downsized, direct-injected and turbocharged engines in its lineup to minimize fuel consumption.

Stop-start systems are also starting to make an appearance, with some manufacturers confident that real-world gas-mileage benefits for consumers will compensate for the fact that the effects stop-start systems are minimal in EPA test cycles.

Several current models--even the Toyota Prius, which has an all-new model coming in the next year or two--already beat the 42-mpg window sticker figure.

That's led many to believe that hybrids and plug-in vehicles will be the only way to hit such economy targets. But Kesseler's comments suggest they may not be.

He says manufacturers must work closely with suppliers of the touted technologies, to keep up development momentum. If they do so, he says, judicious application of these technologies could bring regular vehicles well within reach of 2025's targets.

The challenge for automakers will be to ensure these new, high-tech engines deliver acceptable real-world mileage, rather than testing-optimized figures.